Directional radio receiver



Jan. 8, 1946. w. P. LEAR 2,392,328

l DIRECTIONAL RADIO RECEIVER Filed Aug. 24, 1943 2 Sheets-Sheet lWilliam 5? ear N LA l?? in H for:

INVENTOR ELM/45M ,Zn/v ATTORNEY.

Ja'n. 8, 1946. w. P. LEAR 2,392,328

DIRECTIONAL RADIO RECEIVER Filed Aug. 24, 1943 2 Sheets-Sheet 2INVENTOR. Ul'blarn l? aan BY ./Jv ATTORNEY.

.-Qamopos. P.,

bumen: o

NN, GN..

Patented Jan. 8, 1946 DIRECTIONAL RADIO RECEIVER William P. Lear, NorthHollywood, Calif., assignor, by mesne assignments, to Lear,Incorporated, Grand Rapids, Mich., a corporation of Dlinois Continuationof application Serial No. 291,807, August 25, 1939. This applicationAugust 24, 1943, Serial N 499.754

(Cl. Z50-11) 14 Claims.

This invention relates to receiver arrangements for radio guidancesystems for mobile craft, particularly aircraft. The present applicationis a continuation of my copendng application Serial No. 291,807 ledAugust 25, 1939, and assigned to the same assignee as the present case.

The receiver arrangement of the present case is designed to operate inconjunction with a pair of non-directional radio signal transmittersarranged in spaced relation along an approach path such as an airportrunway. The receiver arrangement continuously indicates to the pilot hisexact relative lateral position with respect to the airport in general,and his exact position with respect to the approach path to the runway.As described in my said copending application, with the system of myinvention, the pilot may approach the runway directly on the shortestroute and without any trial flight since he clearly knows hisorientation with respect to the airport and runway course. The twoindicator needles of the receiver are in line with the center-zero indexwhen the pilot is on-course with the runway. As he passes over the outertransmitter, the out" indicator needle reverses by 180. This serves as amarker indication to appraise him of his exact distance from the edge ofthe runway. As the pilot continues on-course to the runway, the secondor in needle will reverse by 180 when he passes over the innertransmitter station. No separate marker beacons are thus necessary. Thepilot is then ready to glide down to a landing using any suitablevertical guidance means.

Drifting from the predetermined approach course is accurately detectedthrough the dual indicator readings, and is readily compensated for thepilot. No reliance on directional gyroscopes or other flight instrumentsis necessary. The results are foolproof and independent of adverseweather conditions. There are no successive receiver tuning changes orother distracting duties required of the pilot with the system of myinvention. After the initial tuning operation, the dual indicatorarrangement is continually effective in guiding the pilot in the mannerset forth.

In a preferred form of my invention I employ two transmitter stationshaving the same carrier frequency. The radiation by the stations issuccessively switched on and off at predetermined intervals. The twostations are differentiated with either separate audio frequency tonemodulations, or with one station being tone modulated and the otherumnodulated. A dual automatic directional indicator system lis usedaboard the mobile craft, In one form the receiver system has twoseparaterotatable directional antennae, one corresponding to each of the two eldtransmitters. An automatic radio control unit is used to individuallyorient the two directional antennae to their null signal positions withrespect to the radio transmitters".

The directional antennae are operative over a 360 range. A separateautomatic control radio unit may be used for each of the rotatable loopantennae. In a preferred embodiment, I use a single automatic radiocontrol unit connected successively to each of the two rotatabledirectional antennae in correspondence with the intervals of radiationof the transmitters as controlled by the audio tone modulations thereof.A composite indicator is used, having two needles, one coupled to eachof the rotatable antennae. The two needles point out the actualdirection towards each of the field transmitters, and appraise the pilotof his exact lateral position with respect to the airport and theapproach path to the runway as will be described in more detailhereinafter.

The present invention is applicable for guiding a marine vessel into itsslip, such as during fog conditions. In this case, the two radiotransmitters are placed on land in line with the direction which thevessel is to enter the slip. The pilot employs the same approachequipment described in connection with the aircraft guidance and isaccurately guided into the slip despite river current or zero visibilityconditions. Anti-collision devices can be used for safety reasons whenthere is sole reliance on the radio guidance in docking the vessel.

It is therefore among the objects of the present invention to provide aradio receiver arrangement for indicating to the pilot his exactrelative position with respect to two spaced transmitter stations; toprovide such a system including two directional antenna, means fororienting the antenna with respect to received radio signals, adirectional control unit, a composite indicator having needlesoperatively associated with each antenna, and means selectively operablein response to the received radio signals for intermittently connectingeach antenna and its orienting means to the directional control unit; toprovide a dual radio directional guidance system for givingsubstantially continuous bearing indications on each of a pair of spacedradio transmitters; and to' provide a novel radio instrument approachsystem employing a plurality of rotatable directional antennaautomatically controlled from a unitary directional control receiver.

These and further objects of my present inthrofugh connection leads |36.

vention Will become apparent from the following description andaccompanying drawings.

In the drawings:

Fig. 1 is a diagrammatic arrangement of a cornplete receiver systemincorporating the principle of the present invention.

Fig. 2 illustrates one form of the dualY indicator mechanism, beingpartly in section.

Fig. 3 is a schematic electrical diagram of a preferred circuitarrangement for the automatic directional receiver equipmentcorresponding to |22' connect the Winding 0f loop antenna |20' torelayarmatures |24 -and |25.

Relay armatures |25 and |21 are employed for selectively connetcing thecontrol motorfdriv'e arrangement for the loop antennae tothe receiver.Relay` solenoid is arranged to actuate relay leads 23" for connection tothe front contacts of armatures |324 to |21 when energized bycurrentsfrom the automatic directional receiver system connected theretothrough leads |29. The position of loop antenna systemZ is controlled byreversible motor |3Il connected to loopy shaft I2| throughelectromagnetic clutch |32 and gearing |33, |34. Motor |3|is connectedinipara'llel with magnetic clutch V|32 and in turn to thev back contactsof relayarmaturesil26,` |21 by leads |35.

The motor control system of rotatable loop antenna i20" comprises motor|3|" connected toA shaft |2| through electromagnetic clutch Y|32"andg'ears |33', |734. Motor 13|' and clutch |32" are connected acrossfront contacts of relay armatures |26, l'lthrough leads |35\. Relayarmatures |125, |21 are connected to the motorro-v lay ,system of theautomatic directional unit The preferred constructionofY the rotatableloop antennae |20,

|20 Vand their associated electromotive d-rives isv preferably inlraccordance with the disclosure of` myPatent No. 2,308,521 4issuedJanuary "19, 1943 entitledV Automatic radio direction indicator. Theautomatic radio directional receiver sche-e' matically illustrated inFig. 1 is preferably similar to-thatdisclosed in my said patent modifiedto perform the radio guidance operationV inV connection with the twoloopsystems. Relay armatures |24 through |21 are normally attracted totheA upper or front contact position shown through norm'al continuousenergization of relay solenoid|30. With the relay armatures in the upperposition, loop antenna |20 is in circuit connection with the automaticradio directional circuit through leads |28, land its associated motorand clutch |31', |32. i5 also connected theretoY through-leads |36.

'he'receiver system normally operates in this position as an automaticdirectional receiver indicating the bearing onany radio station tuned inby the receiverunit. Ai loop position ltransnfiitterY unit |40 isemployed to .transmit the angular position yof loop antenna |25 toremotely located meter |45. A direct current vSelsynv telemeteringarrangement incorporating a batteri/14| and three-Wire cable |42 is usedin the embodiment of Fig. l. Needle 2 of meter |55 is associated withrotatable antenna |20' and indicates its angular position on the scaleof meter |45.

When the automatic receiver is to be used for instrument approach inconjunction with spaced field transmitter stations such as indicated inFigs. 1, 4 and 5, of my copending application Serial No. 291,807, thedirectional receiver circuit is tuned to the predetermined frequency ofthe transmitters. In this case, directional antenna |20 will be movedtopoint so that its null signal position corresponds to the directiontowards the unmodulated transmitter station and out indicator needle 2of Vmeter |45 will thus point towards the unmodulated station.The'automatic angular orientation of loop |20 through control motor |31'is effected during the transmission interval of the unmodulated station,within onethird of a second in the prefered case.

During the transmission of the in station, the predetermined audiofrequen-cymodulation of the radio frequency carrier Wave at such stationwill cause relay |30 to be deenergized in a manner toV beV described,and.' relayarmatures 5.12.4...to` |21 `will drop to the back contactposition. Thus,

a bearing ronthe tone modulated station. D. lC.`

Selsyn transmitter' |40'. is energized by battery |4| and connected tometer |45 through cable |42. Loop antenna- |20 is automatically moved.so that its null signal positionraccurately. corresponds to thedirection towards'I the tone modulated station;

needle 2; The-Zero indexv 0 corresponds to the airis of thel aircraft.After adjustment of the tun-4 ing of the directional receiver to thecommon car' rier frequency of' both transmitting stations, in?Y strumentapproach guidance as described in connection with' Fig. 1 of my saidcopending application.V Serial No. 291,807 is effected. The altere*nately radiating transmittingor field stations causer relay soleno'd |30to correspondingly switch rotatable antennav system' |20 and alternatelysystem |20 'out of andV into vcircuit relation with the automaticdirectional receiver. The arrangement is such as to successively movethe respective antennae'and their associated` needles on indicator r| topoint out, preferably to within 1' of arc,rthe direction towards therespective eld stations.

The preferred automatic directional receiver, commento both'rotatableloop antenna systems,

is shown inblock diagram in'Fig'. 1 nand Vcerro-.

I of indicator' radio frequency receiver |53 are demodulated andimpressed upon audio frequency amplifier |55. During the transmissioninterval of the unmodulated transmitter, no separate tone or audiofrequency relay signal is derived and relay solenoid |30 remainsnormally energized attracting relay armatures |24 through |21 asindicated in Fig. 1. However, during the transmission interval of theradio transmitter modulated by a relay tone, say of 75 cycles, a.corresponding 1.5 cycle note will appear at the output of audiofrequencyamplifier |55l The 75 cycle tone is impressed upon relay filter|58 which prevents the passage of other frequency signals and passes thepredetermined relay frequency of 75 cycles in the present The output oflter V|58 is connected to relay rectifier |59, the output of which isconnected to solenoid |30. A preferred arrangement for the actuation ofsolenoid |30 is such that the solenoid is normally energized connectingloop antenna system to the directional receiver. Upon reception of aradio signal bearing a substantial 75 cycle (or other predeterminedfrequency) signal relay is arranged to be deenergized and switch thedirectional receiver from directional antenna system |20' to directionalantenna system |20. It is to be understood that the relaying actionwherein the predetermined (75 cycle) note causes energization of relay|30 instead of deenergization thereof may equally well be employed.Detailed circuit diagram Fig. 3 illustrates the arrangement foreffecting the herein described operation of relay solenoid |30 by the 75cycle signal.

The loop winding relay armatures |24, |25 are coupled to the loop radiofrequency amplifier |60 through radio frequency transformer IGI, |62 bytransmission cable |28 which is preferably of low impedance. A variablecondenser |63 in shunt with the secondary winding |62 is used to tune-in4the desired radio station. vAll the tuning controls such as condensers|54 and I 63 are preferably mechanically ganged together to provide theunitary tuning control. It is to be understood that a plurality ofreceiving bands may be employed to permit operation of the receiversystem over a wide range of radio transmission frequencies. If aparticular frequency is used for effecting the instrument approach to anairport, a rapid switch over means to bring the receiver to thatfrequency may be provided, as will be understood by those skilled in theart.`

In describing theoperation of the automatic directional receiversection, which lies to the right of broken lines |38, reception by oneof the loop antennae is assumed. With the position of relay armatures4|24 through |21 shown in Fig. 1, loop antenna |20 and its associatedcontrol motor circuit are connected to the automatic receiver. Inaccordance with the automatic receiver used in the system of the presentinvention and described in detail in my Patent No. 2,308,521, a loopcontrol signal is provided dependent upon the received loop antennasignal, to operate the motor drive for the loop antenna and rotate it toits null position with respect to the oncoming radio signals. The normalor stable position of the loop antenna is at the null or electricalneutral position with respect to the oncoming radio signals from theassociated transmitted station, giving an exact angular indication ofthe direction to the transmitter of the radio signals. In the presentcase, the unmodulated transmitter is assumed to be radiating forcontrolling the orientation of loop antenna |20' and needle 2. When themodulated transmitter station is transmitting, loop antenna |20 insteadis connected to the system, resulting in a similar electrical action.

When the angular position of the loop antenna |20' is changed from nullduring approach maneuvers, the radio signal is picked-up by the loop andimpressed upon amplifier |60. The magnitude and phase of this signaldepends upon the amount of the off-null angular position of the loop andthe direction of the transmitter to the right or' left thereof,respectively. A local generator |54 of an audio frequency current,preferably of the order of one hundred cycles, is used to modulate theradio signals derived from Vthe loop antenna and producea resultanttoneV modulated radio signal. I prefer to use a tone signal of 102.5cycles as indicated in the drawings, but a different frequency mayinstead be used so long as it is different than the signal for relay|30. Loop signal modulator |65 schematically designates the modulationstage, preferably a balanced modulator, for combining the loop signal of|60 with the tone signal of |64.

The resultant tone modulated radio signal at |60 has a magnitude andphase dependent upon the olf-null position of receiving loop antenna.The tone modulated signal is then suitably combined with thenon-directionally received signal from antenna |50 by a coupling means,such as coupling coil |66 linked with secondary winding |52 of the inputtransformer to radio frequency receiver |53, The nature of the radiosignal impressed upon the input of amplifier 53 is described in moredetail, in connection with Fig. 3 of my said Patent No. 2,308,521. Thesuperposition of the non-directional radio signals with the locallymodulated loop signals provides a resultant radio signal with the 102.5cycle tone component having a magnitude and relative phase dependentupon the off-null position of the loop antenna with respect to theoncoming wave. Radio frequency receiver |53 may be a tuned radiofrequency circuit or a superheterodyne circuit. The receiver unit |53contains a demodulator or detector for the audio frequency components ofthe amplified radio signals. The audio frequency signals at the outputof unit |53 comprise modulations of the original radio wave plus the102.5 cycle tone or control signal obtained when the loop antenna is olfnull.

An audio frequency amplifier |55 is connected to the output ofreceiver-detector unit |53. Ampliner |55 supplies audio unit |56 withsuiiicient energy for operating headphones oonnectable to jack |51 atthe output thereof. The output of audio frequency amplifier |55 is alsoconnected to a separate control signal amplifier |61 through a suitablephase shifting net-Work |68 and 102.5 cycle pass lter |09. The 102.5cycle tone signal is thus filtered out from the output of audiofrequency amplifier |55 and amplified a substantial degree for use as acontrol signal to operate the relay control tube system indicated at|10. The relay control tube system is energized by both the controlsignal from amplifier |61 as well as the correspondingly amplified tonesignal obtained directly from generator |64 and intermediate toneamplifier |1|. Details of the operation and interrelation of therespective control signals and the relay control tube system |10 aredescribed in further detail in connection with Figures 4 and 4a of myPatent No. 2,308,521.

Control relays indicated at |12 comprise solenoids |13 and |14 connectedto the relay control -|2|'- and associated gearing.

either relay |13 or |14` is determined upon thetube system,|1|l.ASolenoidsz|13and |15 areselectively energized Vfrom control system- |10-in laccordance with the angular position to the right or left oftheloopconnected, yWithrespect to the direction of the oncoming radiowaves. When relay |13 isenergized, it attracts its armature |15 to-`close the electrical circuit through ground -in-y cluding its frontcontact, batteryY |11, Vand the loop motor. When antennav is connectedto the system, motor |3 is thus energized. Motors |3| and -|3|f areconnected in a predetermined manner to operate-in the direction torotate loop antennae |20 and |20" respectively towards their null signalposition through their shafts '|2| `and Energization l of direction ofthe angular deviation of the connected loop antenna (|20) from its nullposition with respect tothe-radiating station. so-that thev contactposition, deenergizing and stopping thel associated motor.Electromagnetic clutches |32 and |32 are electrically' shunted across ltheir motor. energization circuits to immediately disconnecttheassociated motor from` the loop antenna-insuring a rapid stop-of theloop rotation at the time of motor deenergization, and eliminatingY the.possibility of overshooting or overdriving bythe motor dueto itsmechanical inertia; The frictional forces of the gearing and-thebearings of` theloops are generally suiicient to quickly stop the, looprotation.

In practice I have constructed systems in accordance-with the presentinvention Whichautomatically operate the loopsand therefore theassociatedbea-ringindicators at a rate of 180 and more per second.-v Theaccuracy :of the lresultant bearing may readily be made within 1 of arc,i, e. theA actual directional indicationV on each radio transmitterbeingcorrect to-within 1 or less.V The-bearing indications arefon a360"` dial andamove` -to the stationary bearing position through theshorter angular path. I prefer a rate of indication of about 125 persecond for the one-thirdv of a second transmitterl radiation periods.

When theloop antenna reaches, cris substantially at, its nullsignal-position a zero or substantially zero magnitude radio frequencysignal isyimpressed upon radio frequency amplier |60 for modulation at|65 by the generated .tone signal from. |65.v The magnitude of thecontrol signalfrom amplier accordingly is-also zero, or

substantially `zero atthat time, and control relays |12v are in thedeenergized position shown. The

loop accordingly remainsstationary when it is at ergized by the oncomingradio signal from thel transmitter, and impress it'fupon amplifier |60witha magnitude and phase relation correspond- F escasas Y ing to thealtereddirection thereof, Should the` deflection ofthe aircraft causethe loop toreceive a signal of phase corresponding to that whichvenergizes solenoid |13, the abovedescribed operation. of-the loopmotorie repeated to bring the-loop to the new null signal position.Should, however; the aircraft turn so that the loop-is deviated in theAopposite angular direction,- the phase of the control signal impressedupon relay control tube system Y|10 will be different by 180"n andenergize solenoid |14 instead.

When solenoid |14 is energized, its armature |16 is attracted to the.front contact to electrically` complete the connected loop motorcircuit'including its-associated clutch, ground, andbattery |11.Electromagnetic clutch |32' is, thereupon immediately engaged and motor|3|' is -rotated in the direction oppositeto that corresponding'to itsvenergization by solenoid |13 when loop system |20' is in connection withthe receiverv aS shown in Fig. 1. Motors |3| and |3| arege versible inthe Apresent case, kand are not neces sarily a direct current type.Relay armatures |15 and |16 are arranged so that the directiony ofcurrent flow throughthe connected motorie selectivelyreversed to causethe motor to rotatev its.` associated, loop Vtowardsits null signalposi1 tion in the shorter path of rotation. Thus, when solenoid |14 :isenergized, the motor will rotatein a direction opposite to that due` toenergizetion ofrelay |13. Y.

An important feature ofthe preferred automaticdirectional receiverresides in the fact that, for any bearing, the loop antennae arel attheir electrically neutral and geometric null positions, and remainstationary for the duration of the bearing. Furthermore, no sense ordirectional ambiguity occurs, and the null positionwhich the loopassumes is4 accurate for `any bearing on the transmitters. Pointer 2 ofindicator |45moves in. exact correspondence-with loop antenna |20' andis arranged to point to the center zero posi` tion 0 shown on the dial,when the open planeof loop |20' is perpendicular to the longitudinalaxis of the aircraft. Similarly, pointer orneedlemovesin exactcorrespondence with loop an tenna |20, pointing to: center zerowhen the`plane of loop |20 is 'perpendicular to the flight direction.

The accuracy of indication is independent ofl the position -of indicatorneedles I and 2 since any reading thereof corresponds to fan electricalnull position of loop antennae* |20 and |20", and'no balancingrofelectrical :parameters orsignal components are required to maintain thereadings. The interpretation of the readings; is readilyapparent tothepilot, andhe eflectsan instrument approach asidescribed in connectionwith Fig.V 1

of vmy said copending application Serial No.`

rent Vloop positiontransmitter of thesecond loopA system. Three-poledouble-throw switch vr| is used to connect leads |83 with cable |83 asshown indotted during the double indicator instrument telemeteringmanner.

Aapproach operation of the system so that both needles and 2 of meter|45 are independently controlled.

Indicator needle I is connected to central spindle |86 pivoted in endbearing |81. Magnetic core |88, shown in dotted, is secured tospindle|86 and arranged to magnetically coact with the interior of annularwinding |8| in the usual Indicator needle 2 is coupled to the end oftube |90 concentric about spindle |86. Tube |90 is rotatable ondiagrammatically indicated bearing |9| for independent rotation withrespect to spindle |86 of needle Magnetic core |92, shown dotted, ismechanically secured with rotatable tube |90, and is magneticallycoactable with annular winding |82. Indicator needles and 2 are coaxialand independently controlled to assume the angular positions of the twoloop antenna systems during the instrument approach maneuvers described.A casing |93, having a ange |94, fitted within the open end of housing|80, encloses indicator needles l and 2 and contains the scale for theindications. A transparent window |95, such as glass, is tted into thetop end of enclosure |93.

When the dual receiver system is to be used for taking fnormaldirectional bearings on only one transmitter station and not for thedescribed twostation instrument approach maneuvering, threepole switch|85 is thrown to the position drawn in solid lines in Fig. 2 connectingannular windings |8| and |82 in parallel. Both indicator needles and 2then act in unison, one above the other, and each assumes the sameangular position on the scale of meter |45. For ordinary automaticdirectional operation, both sections of the meter are connected inparallel with one of the loop position transmitters and give the samereading.

Accordingly, when the dual indicator of Fig. 2 is in circuit with a dualreceiver system in accordance with the present invention, three-wirecable |84 connects to the position transmitter of the loop antennanormally in circuit with the receiver, and three-wire cable |83' to theloop position transmitter of the other antenna. For example, if used inthe receiver system of Fig. 1, cable |84' would correspond to cable|42', connecting t position transmitter |40 of loop antenna systemnormally connected to the re-A ceiver through relay armatures |24 to|21; and cable |83' would correspond Ito cable |42 connecting toposition transmitter |40 of antenna system |20. Three-pole switch |85 isoperated to the solid position for both needles of indicator |45 to givea single reading when the automatic directional system is used for radioguidance in general, and is connected to the dotted position when thepilot is ready for instrument approach to a runway having stationscorresponding to T1 and T2 of Fig. l of my copending applicationSerialNo. 291,807 when both needles become independently operative inthe manner described.

Fig. 3 is a detailed schematic electrical diagram, partially in blockform, of a commercial form of the automatic receiver system constructedin accordance with the principles of my present invention. Relay system|24 through |21 selectively connects the two loop antennae systern |20and |20' to the receiver as shown in Fig. l. Fig. 3 is a specificelectrical showing of the system shown generally in Fig. 1, andrepresents a preferred embodiment thereof though not limited thereto.

Signals from the rotatable loop antenna in circuit with looptransmission cable |28 are impressed upon primary winding |61 of theloop radio frequency input transformer, secondary winding |92 of whichis shunted by tuning condenser |63 and connected to the control grid ofradio frequency amplifier pentode 200 for ampliication and introductionto the control grids of balanced modulator stage |55. The gain of loopamplifier 200 is manually controllable by rheostat 20E connecting thecathode thereof to ground. The anode of amplifier 200 is energizedthrough a shunt radio frequency choke coil 202 connected to the Bsupply.

The output of loop amplifier 200 is coupled to the control grids oftubes 203, 203 of modulator 55 through coupling condensers 204. Thecathodes of tubes 203, 203 are tied together and connected to groundthrough by-pass condenser 205 and biasing resistance 205. An audiofrequency osciliator |54 comprising two triodes 201, 201 is arranged togenerate an audio or tone frequency currentl of a relatively lowfrequency. The control grids of triodes 201, 201' are coupled to theanodes thereof by condensers 208, 208. Cathcdes of the oscillatortriodes are tied together and connected to ground through biasingresistor 209.

Resistors |98 and |98 are coupled between the grid electrodes of triodes201,201' and ground. Intermediate taps on the resistors |98 and |98'couple a portion of the available alternating current tone energy fromoscillator |64 to the grids of modulator triodes 203, 203 throughcoupling resistances |06 of about one megohm each and through couplingcondensers |91, |91'. Further resistances |99, |99 normally connect gridcoupling condensers |01, |91 to ground to stabilize the 4grid circuitsof tubes 203, 203.

The actual frequency of the tone current generated by oscillator |04 asused in the system is optional, and may for example lie anywhere in theaudio frequency spectrum, or even higher. Practically, however, the tonefrequency should be chosen so as to emciently pass through therespective radio frequency circuits as side-bands, and the audiofrequency circuits as well, be audible to the pilot when present anddiffer from the relaying tone from the eld transmitters. It is alsodesirable to prevent interference with theintelligibility of the auralmessages of the ,radio signals. An important consideration is tominimize any effect due to the sound modulations of the radio wave uponthe control circuit. I have found that a control signal in excess of 200to 300 cycles contains sound modulation components after filtering outfor control purposes.

Modulation kicks occur when the sound frequencies of the radio signalscoincide with the control frequency, and interfere with the stability ofthe directional indications. A tone frequency of the order of 100 cyclesis suciently high to efiiciently pass through the radio and audiofrequency channels of the system, sufciently low to not interfere withthe intelligibility of the audio frequency modulations of the radiosignal, and is not effected by modulation kicks. A practical tonefrequency in this range I found to be a tone of 102.5 cycles, asindicated in the figures. This frequency is satisfactory when the looprelaying frequency of the tone modulated transmitting station is '15cycles. The field transmitter tone should differ sufficiently from thereceiver control frequency, 102.5 cycles in the present case, to beproperly filtered out of the audio output circuit. Thus 75 or lesscycles, or

Yshunted there-across.

150 or more cycles per `second are satisfactory for. the tone modulatedtransmitting station when 102.5 cycles are used in the receiver.

Control grid electrodes of modulator triodes '203,V 203' accordinglysimultaneously receive the audio frequency tone signal from oscillator|64 and the radio frequency signal picked up by the connecteddirectional antenna. The output of modulator stage |65, obtained throughthe anodes of tubes 203, 203', is connected to opposite sides of radiofrequency winding |66 coupled to secondary winding |52 of thenon-directional antenna circuit. The anode supply for modulator tubes203, 203 is obtained through a center tap on winding |66 connected tothe common B supply as indicated.

The frequency of the loop modulated signals is the sum and difference ofthe received radio signals and the low frequency oscillator tone signal.directional radio frequency signals with the tone modulated loop signalsupon winding |52 produces a resultant signalv upon the control grid ofradio frequency amplifier 2|0. The non-directional signal'from, antenna|50 serves as a reference signal or :sense determinator, so that theright or left sense of the loop antenna signals is established forfurther control action on the orientation of the loop antennae. Thusproper functioning of the automatic directional receiver is assured,quickly bringing the connected lcop antenna back to 'its null signalposition to give accurate bearing indications on the fieldstationtransmitting. Y

The signals impressed upon the control gi'idlz` of radio frequencypentode 2|0 are amplified and The simultaneous induction of the nonshownin block'diagram form.4 The anode indicated at 236 .of 'outputstage ofintermediate 'frequency amplifier 235 is connected to transformer 231,the primary and secondary windings of which are respectively shunted byadjustable condensers 238 and 239 and tuned to the intermediatefrequency. An audio frequency detector stage 240 has its control gridconnected to the output of intermediate frequency transformer 231 fordemodulating the signals and produce corresponding audio frequencycurrents across cathV ode resistor A245 connected to ground.

Both the radiosignal tone modulations as well as the local controlsignal if present, produce a corresponding .audio frequency signalacross resistor 245 vby the detectoraction.V The anode ,of detector r240is connected to the common B supply as indicated. Condenser 246, betweenthe i cathode of detector 240 and ground,Y by-passes Y audio frequencysignal modulations von the radio transmitted through voutput radiofrequency transformer 2|| havingv its secondary winding tuned toresonance by variable condenser 2|2 The output of transformer 2H iscoupled to intermediate grid electrode 2|5 lof the radio frequency mixerstage 220 vthrough coupling condenser 2|6. Radio frequency mixer stage220 is shown as a hexode wherein grid electrode 2|1 adjacent to thecathode is energized by a signal emanating from a local beat frequencyoscillator 22| operated in the usual manner for superheterodynereception. The anode and screen grid operating potential for stage 220isv supplied through respective resistors 222, 223.

The output of radio frequency mixer stage 220 comprises primary-Winding225 of a step-down intermediate frequency transformer shunted byadjustable condenser 221 for resonating the coil-Y 'attheintermediatefrequency, such as 455 kilocycles. Transformer 225, 226 is .a step-downtransformer sol that a long low impedance transmission line 230 may beused to permit placing the intermediate frequency `and audio frequencyVamplifier equipment remote from the radio frequency section includingdirectional and nondirectional radio signal amplifiers, and loopVmodulatcrstage. Transmission cable 230 is an electricallyshielded lowimpedance cable terminatingin a correspondingly low impedance primaryrWinding 23| "of step-up intermediate frequency transformer 23|, 232.Secondary winding 232 of `the terminating transformer isshunted by aresonating adjustable condenser233 to tune the transformer to theintermediate-.frequency used. The output of step-up intermediatefrequency transformer 23|, 232 isconne'cted to the grid electrodeindicated at 234 of the input stage of two-:stage intermediate frequencyamplifier 235 carrier lwave and the control or tone signalampliiiedtogether therewith, are impressed upon two-stage amplifier 260 forfurther amplification to an appreciable signal level. AThe outputcfamplifier 260 is coupled to the aural amplifier indicated at 21,0, itothe output of which earphones 215 areconnected. The pilot .adjusts theaural level of the ,signals by a separate manual control in aural unit210. The output of Vaudio frequency amplifier 260 is also coupled to-amplifier stages 280 and 290 for selecting and further amplifying .the102.5 cycle loop ymotor contro signal and impressing it upon relaycontrol system |10, and also Ato pass filter 350 for controlling theselective connection of loop systems |20 and |20' to the receiver,through transmitted relaying signals. f

The output of audio frequency amplifier V260 is coupled to the control-grid 20|v of amplifier stage Y280 vby coupling .condenser 26| and phase.shifting net-work 262,

263. Resistor 265 is 'shunted across phase shifting network 262, 263

connecting the control vgrid of stage 280 to ground. The relativeimpedance of resistor 262 and condenser263 `is chosen to suitably shiftthe phase of the 102.5 cycle control signal to be impressed upon`control grid 28| to' compensate for anymisphasing thereof caused in thecircuits prior to that point.v Such phasing is made to cause the Yphaserelation cf the ignalarri ing at the input of tube relay control system|10 to iba-substantially in-phase or 180 out-of-phase with the.correspondingly impressed tone signal `from amplifier I 1|.

The control signal impressed upon controlgrid electrode 28| of pentodeamplifier stage 280 is amplified in a conventional manner. The output ofamplifier 280 is impressed upon control grid 29| of a further amplifierstage 29D through coupling condenser 282. A tuned filter 285, 288 is.used to filter out other signals or modulations than the 102.5 cycles,and most efficiently pass this signal frequency. Other filterarrangements than the shunt ,choke coil 285 and condenser 283 maybeused. Amplifier stage 290 comprises a triode tube, the anode circuit ofwhich includes primary winding 292 of audio frequency couplingtransformer 235. Secondary winding 233 of transformer 295 is shownschematically coupled to the input of the relay contro1 system |10. Theoutput of 102.5 cycle amplifier |I| is impressed upon relay controlsystem |10. Fig. 4 of my said Patent No. 2,308,521 illustrates apreferred circuit arrangement for the relay control tube system |10.

Variations in the level of the received radio signals are compensatedfor by an automatic level control. A further arrangement of the systemmaintains constant the anode or B voltage 'supe ply for critical partsof the circuit despite varia tions in the supply voltage thereto, toinsure uniform sensitivity and operation 'of the loop motor controls andassociated electronic relay system. A voltage regulator tube 350 isconnected between a particular point 305 and ground, to maintain apredetermined and uniform operating voltage supu ply for the criticalpart of the electronic control arrangement which includes the anodes ofoscillator |64 through lead 304, the amplifier l| through lead 301 andelectronic relay system |13 through lead 306.

An automatic level or volume control arrange ment is provided throughrectifier 3m fed by an intermediate frequency signal tapped fromintermediate frequency output anode 235 through coupling condenser 3||to anode 3|2 thereof. Delayed automatic volume control (D. A. V. C.)action is obtained by providing a positive biasing voltage raising thepotential of cathode 343 to delay the biasing control action till thereceived radio signals reach a predetermined level. Anode 3|f2 ofrectifier 3I0 is connected to the control grids of the respective radiofrequency, intermediate frequency and audio frequency stages of thecircuit to establish a substantially fiat and uniform amplificationresponse ofthe signals through the system.

Coupling resistances 3|5, SI5, 3|?, 3|8 are used in this level controlcircuit, and control grid 236 of the intermediate frequency amplifier isconnected thereto by direct connection 3|9 through f secondary winding232. The second stage of the intermediate frequency amplifier 235 isprefera ably also controlled by the level control circuit described. Theinclusion of at least the first audio frequency amplifier stage 250 inthe signal control circuit from rectifier 3|0 results in a very fiatoverall response despite wide signal level changes in the received radioWaves.

A manual switch 323 is provided at the cathode of the first radiofrequency amplification stage 2|0 to disconnect the automatic volumecontrol effected thereto through resistor SI5, for manually controllingthe bias through variable resister 322 in the cathode circuit. Thismanual volume control is useful for communication or reception of radiorange signals. A further switch 325 is provided for continuous wave beatfrequency oscillator 330 to connect it to audio frequency detector stage245 for heterodyning continuous waves. Continuous Wave oscillator 330 isused for audibly perceiving continuous wave transmission and serves as asignal station finder for such stations. The normal connection o switch325 to ground contact 325 is schematically indicated for renderingoscillator 330 ineffective as a heterodyning means, which connection isused for phone reception. By ungrounding switch 325,

oscillator 330 becomes eiective for heterodyne reception of continuouswaves.

A direct current millemeter 353 is connected between the output ofautomatic volume control stage 310 and ground, through series resistance345. Meter 330 serves as a' measure of the automatic level biasingcurrent and indicates the relative signal strengths of received radiosignals. Meter 340 thus serves as arelative distance or millemeter.Flight toward a station increases the signal strength and therefore theindication on meter 340. Flight away from a station correspondinglydecreases its indications.

The audio frequency output of amplifier 260 is connected to a highlyselective filter 350 by leads 345 to segregate the radio relayY tonef'lcycles V in the present embodiment, from other audio frequency signalswhich may be present. Pass filter 350 is selected to pass efficientlythe chosen relaying frequency. The actual construction of pass filter350 is optional, and I have illustrated one form which it may assume inpractice. A resonant shunt path comprising inductance 35| andcapacitance 352 tuned to the frequency to be passed, comprises theinitial section thereof. A series inductance 353 connects shunt path35|, 352 to a further shunt path 354, 355. The output of filter 350contains series inductance 356.

Filter 350 is specifically designed to reject the 102.5 motor controlfrequency which orients the loop antennae. The invention is not limitedto any particular frequency for either the loop motor control or therelay switching control. The output of filter 350 is coupled to arectifier arnplifer stage 350 through coupling condenser 351. The '75cycles signal is impressed upon detector anode 358 having shunt resistor359 to ground across which the rectied component isbuilt up. The cathodeof stage 350 is positively biased with respect to ground by battery 33|.Control grid 333 of the triode section of tube 360 is coupled to diodeanode 358 through resistor 362. A by pass condenser 36d connects grid333 to ground.

Relay solenoid 35 is connected between anode 366 and the B supply forstage 350. Normal anode circuit current passes through solenoid 355 whenno relaying tone signal is impressed upon stage 360 from filter 350.This current is suiicient to energize the solenoid 365 and attractarmature 310 against contact 339 as shown in dotted. In this `position,relay contact 369 isconnected with armature 310, and energization ofrelay solenoid |30 is maintained through local source 313. Relayarmatures |24 through |21 ac cordingly are normally against their frontcontact position as shown in Fig. 1, connecting loop antenna system |20to the directional receiver circuit.

When the tone modulated transmitter station is operating and the audiofrequency tone modulation thereof is present in the receiver, therelaying tone, namely the 75 cycles frequency signal, passes throughlter 350, is rectified by stage 350 and causes a substantial negativebias upon control grid 363 thereof. The negative bias chokes off thenormal anode current owing through solenoid 365, and permits spring 312to draw armature 310 from contact 359 again-St. backstop 31| as shown insolid in Fig. 3, opening the circuit between battery 3T3 and solenoid|30. When the 75 'cycle relaying signal is received, switch-over relay|30 is accordingly deenergized in the described embodiment. When relaysolenoid |30 Y needle.

disconnecting loop system |20 vfrom the directional receiver andVconnecting loop system |20 thereto.

The switch-over or relaying action by solenoid |30 occurs when the tonemodulated field station is radiating. The altomatic loop orientation bythe directional receiver is made eiective on loop antenna system |20 forthe duration of transmission of the tone modulated station. Loop antenna|20 is quickly moved to its null signal position with respect to thetone modulated station by stable action, bringing the local 102.5 cyclesignal below the value to cause operation of loop motor |3I. Indicatorneedle of indicator M5 (Fig.' 1) corresponds to loop an-tenna |20 and tothe tone modulated station as previously described. Needle I remains atthe position which l antenna |20 assumes after antenna system |20 isunswitched from the directional receiver, upon cessation of the tonemodulated signal and transmission of the unmodulated signal.

In accordance with the operation of the receiver system described, whenthe tonemodulated station ceases transmitting and the unmodulatedstation starts transmitting, loop antenna system |20 is disconnectedfrom the receiver circuit and remains stationary while the other antennasystem |20 is placed under the control of the directional receiver.Signals from 4'the unmodulated station orient loop |20 to point thereto.Needles I and 2 remain. stationary during the quiescent periods of thetransmitters. Since approach maneuvers take place at a speed in therange of 80'to 120 miles per hour,'a switching rate of about one-thirdof a second for -the field transmitters is preferred. I have foundduring extensive experimentation that a rate of switching less thanonehalf of a second gives indications by the needles l and 2 whicheffectively indicate the pilots lat- 'eral position with respect to thetwo landing eld stations. l

The broaderprinciples of my present invention lare not dependent uponthe specific automatic receiver unit disclosed for operating the dualindicator system. However, the success of the invention depends upon theuse of a rapidly operating and accurate automatic directionindica'tingreceiver unit such as I have hereinabove dis- .cing accuracy indirectional positioning of the loop antenna and its correspondingindicator Such rate of operation results in completion of bearings onthe transmitters well within the preferred one-third of a second periodYof transmission of 'the stations.

Although specific embodiment of the invention has been shown anddescribed to illustrate the application of the principles thereof, it

Will be obvious that the invention may be other- Wise embodied withoutdeparting from such principles.

What is claimed is:

1. Avradio directional receiving system comprising tworrotatabledirectional antennae; a single receiver unit, common to both of saidantennae, for automatically orienting a connected sponsive to"successively received radio signals for correspondingly successivelyconnecting Vsaid kdirectional antennae tosaid single receiver unit forindividual orientation to obtain directional bearings on the separatelytransmitted radio signals, one of said directional antenna normallybeing in connection with said receiver unit during inaction of saidrelay means for giving directional bearings on a single transmittedradiolsignal.

2. A radio directional receiving system comprising two rotatabledirectional antennae; a single'receiver unit, common to both of said'antennae, for automatically orienting a connected one of saiddirectional antennae toa stable bearing position with respect tocorrespondingly received radio signals; an indicator electricallyconnected with each of. said directional antennae for pointing out theirangular orientation, said indicators being coaxially arranged; relaymeans' responsive to successively received radio signals forcorrespondingly successively connecting said directional antennae tosaid single receiver unit for individual orientation to obtaindirectional bearings on the separately transmitted radio signals, one ofsaid directional antenna normally being in connection with said receiverunit during inaction of said relay means for giving directional bearingson a single transmitted radio signal; and switching means fordisconnecting the associated indicator from the normally unconnecteddirectional antenna and connecting it with the indicator of saidnormally connected antenna, whereby both indicators give identicalAdirectional readings corresponding to the orientation of said connecteddirectional antenna.

3. A radio directional receiving system comprising two rotatabledirectional antennae; a single receiver unit, common to both of saidan'- tennae, for automatically orienting a connected one of saiddirectional antennae to a stable bearing position with respect tocorrespondingly received radio signals; a dual position indicator havinga pair of indicating elements each connected to one of said directionalantennae for pointing out their angular orientation; and Y a deviceresponsive to successively received radio signals for correspondinglysuccessively connecting said directional antennae to said receiver unitfor individual orientation to obtain directional bearings on theseparately transmitted radio signals, one of said directional antennanormally being in connection with said receiver unit during inaction ofsaid device for giving directional bearings on a single transmittedradio signal.

fl. A radio directional receivingV system comp rlsing tworotatable-directional antennae; a slngle receiver unit, common to bothof said antennae, for automaticallyV orienting va connected one of saiddirectional antennae to a stableA bearv Y ifn'g' position with respectto kcorrespondingly rehizeiyeolV radio signals; an indicator connectedwith eac-hof said directional antennae for pointing out their angularorientation; and relay means' re'- one of said directional antennae toastable bearing position with respect to correspondingly re- Y ceivedradio signals; two position transmitters each connected to one of saidantennae for telemetering its angular orientation; a pair of positionindicators each connected to one of said position transmitters; andrelay means respons1ve to successively received radio signals forcorrespondingly successively connecting saidV directional antennae tosaid receiver unit for individual orientation to obtain directionalbearings `on the separately transmitted radio signals,vone ofsaiddirectional'antenna normally being in connection'with said receiver unitduring'inaction of said relay means for giving directional bearings onasingle transmitted radio signal.

5. A'radio directional rec'eivingsystem comprising two rotatabledirectional antennae; a single receiver unit, common to both of saidantennae, for automatically orienting a connected one of saiddirectional antennae to a stable bearing position with respect tocorrespondingly received radio signals; two position transmitters eachconnected to one of said antennae for telev metering its angularorientation; a dual position indicator having a pair of coaxialindicating elements each electrically connected to one of said positiontransmitters; relay means responsive to successively received radiosignals for corresponding successively connecting said directionalantennae to said receiver unitfor individual orientation to obtaindirectional bearings on the separately transmitted radio signals, one ofsaid directional antenna normally being in connection with said receiverunit during inaction of said relay means for giving directional bearingson a single transmitted radio signal; and switch means for connectingboth of said indicating elements in parallel to the position transmitterconnected to the antenna normally connected to said receiver unit,whereby both indicating elements give identical directional readingscorresponding to the orientation of said connected directional antenna.

6. A radio directional receiving system comprising two rotatabledirectional antennae; a single receiver unit, common to both of saidantennae, for automatically orienting a connected one of saiddirectional antennae to a staple bearing position with respect tocorrespondingly received radio signals; an indicator connected with eachof said directional antennae for pointing out their angular orientation;and a device responsive to successively received radio signals forcorrespondingly successively connecting said directional antennae tosaid receiver unit for individual orientation to obtain directionalbearings on the separately transmitted radio signals, one of saiddirectional antenna normally being in connection with said receiver unitduring inaction of said device for giving directional bearings on asingle transmitted radio signal; said device including a solenoidconnected to said unit, a first set of contacts connected to one of saidantennae and its orienting means, a second set of contacts connected tothe other antenna and its orienting means, and movable armaturesconnected to said unit and operatively associated with said solenoid.

7. A radio directional receiving system comprising two rotatabledirectional antennae; a single receiver unit, common to both of saidantenna, for automatically orienting a connected one of said directionalantennae to a staple bearing position with respect to correspondinglyreceived radio signals; an indicator electrically connected with each ofsaid directional antennae for pointing out their angular orientation; adevice responsive to successively received radio signals forcorrespondingly successively connecting said directional antennae tosaid receiver unit for individual orientation to obtain directionalbearings on the separately transmitted radio signals, one of saiddirectional antenna normally being in connection with said receiver unitduring inaction of said device for giving directional bearings on asingle transmitted radio signal; said device including a solenoidconnected to said unit, a first set of contacts connected to one of saidantennae and its orienting means, a second set of contacts connected tothe other antenna and its orienting means, and movable armaturesconnected to said unit and operatively associated with said solenoid;said solenoid normally being energized to 4 retain its armatures inengagement with one set of contacts to normally connect said one antennato said unit. v

8. A radio directional receiving system comprising two rotatabledirectional antennae; a single receiver unit, common to both of saidantennae, for automatically orienting a connected one of saiddirectional antennae to a staple bearing position with respect tocorrespondingly received radio signals; an indicator electricallyconnected with each of said directional antennae for pointing out theirangular orientation, said indicators being coaxially arranged; a deviceresponsive to successively received radio signals for correspondinglysuccessivelyV connecting said directional antennae to said receiver unitfor individual orientation to obtain directional bearings on theseparately transmitted radio signals, one of said directional antennanormally being in connection with said receiver unit during inaction ofsaid device for giving directional bearings on a single transmittedradio signal; said device including a solenoid connected to said unit, al'irst set of contacts connected to one of said antennae and itsorienting means, a second set of contacts connected to the otherantennae and its orienting means, and movable armatures connected tosaid unit and operatively associated with said solenoid; said solenoidnormally being energized to retain its armatures in engagement with oneset of contacts to normally connect said one antenna to said unit; andswitching means for disconnecting the associated indicator from thenormally unconnected directional antenna and connecting said associatedindicator with the indicator of said normally connected antenna, wherebyboth indicators give identical directional readings corresponding to theorientation of said connected directional antenna.

9. A radio directional receiving system comprising two rotatabledirectional antennae; a single receiver unit, common to both of saidantennae, for automatically orienting a connected one of saiddirectional antennae to a stable bearing position with respect tocorrespondingly received radio signals; a dual position indicator havinga pair of indicating elements each connected to one of said directionalantennae for pointing out their angular orientation; relay meansresponsive to successivly received radio signals for correspondinglysuccessively connecting said directional antennae to said receiver unitfor individual orientation to obtain directional bearings on theseparately transmitted radio signals, one of said directional antennanormally being in connection with said receiver unit during inaction ofsaid relay means for giving directional bearings on a single transmittedradio signal; said relay means including a solenoid connected to saidunit, a rst set of contacts connected to one of said antennae and itsorienting means, and movable armatures connected to said unit andoperatively associated with said solenoid; said solenoid normally beingenergized to retain its armatures in engagement with one set of contactsto normally connect said one antenna to saii unit.

l0. In a radio guidance system incorporating two spaced and successivelyradiating transmitters having the same carrier frequency with thesignals of one transmitter being tone modulated, two rotatabledirectional antennae; a receiver unit for automatically orienting aconnected one of said directional antennae to a stable bearing positionwith respect to correspondingly received radio signals,V said receiverunit being tunedjto the common carrier frequency of the two successivelyradiating signal; transmitters; an indicator connected with each of saiddirectional antennae for pointing` out their angular orientation; one ofsaid directional antennae normally beingl in connection with said,receiver unit duringv receptionA by said unit of unmodulated. signalsfrom one of the transmitters for giving. directional bearings on asingle transmitted radio. signal; and selectively operable meanseiective upton reception by said units of tone modulated signals fromthe other transmitter to connect, the. other antenna to said unit forobtainingindividual bearing indications on each of the transmitters;

11;. In a radio guidance system incorporatingtwo.. spaced andsuccessively radiating` transmit.- ters having the same carrierfrequency with the signals of one. transmitter being tone modulated, tvvo rotatable directional antennae; a receiver.. unit for automatically orienting a connected one of saidv directional antennae to a stablebearing position with respect to correspondingly received radio.signals, said receiver unit beingY tuned to thecommoncarrier frequencyof the. two successively. radiating signaltransmitters; an indicatorconnected with each of said directional antennae. for oointing out theirangular orientation; one) Qff-Safldrcicnal. entennanormally beingincon--` nection with said receiver unit. during reception.. by said unitof unmodulated signals from one of the transmitters for giving:directional bearings on a single,Y transmitted radio signal; a. devicellcllldiligi asoloncidoonnected tosaidunitiarst.

rnittersJV andI selectively operable means. effective..

iipolrreoeption; by saidf units...of. tone modulated; signals from theother transmitter.. to. eiect de;-eocigiaaiion.orSaidsolenoid.toconnecttne other. antenna toV said unitfor. obtaining.individual;v bearing indications onA each of thetransmitters.

l2t In; a4 radio.Y guidance system. incorporating two spaced andlsuccessively radiating. transmit; tershaving the same` carrier frequencywith. the

` signalsof one transmitter. being. tone modulated,

two rotatable directional antennae; a. receiver.

unit for automatically orienting a. connectedlone.

or. saidfdirectionalantennae to estable bearing.

- position Withrespectto correspondingly received radio signals, saidreceiverunitbeing tuned toA the common carrierA frequency of the. twosuc-v cessively radiating,y signal transmitters; an?v indi.- c atorconnected with each of said, directional an-v tennae for pointing outtheir angular; orientation; one of saidv directional antenna;normallybeing. inconnectioniwith said receiver. unitduring.

reeentionfby. said unitv of unmodulatedlsignals..

from.v one of` the transmitters for giving directional bearings onasingle transmitted radio, signal; a deviceY including aY solenoidconnected tofsaid unit, a rstlset of contacts connected-to.. one. ofsaid antennaeandits;orienting..means, ay second set of contactsconnected; to the. other ane torinaVv and'. its orienting meanaandzmovable; ar.. matures. CQlIieCtEd 11.0 Seid urlt.. andoperatively,

noid to... connect theother antennatoesaidaunitforf obtaining.individual: bearing; indications on: Yeacn` ortho transmitters" 1-3.,In; a radio guidancesystemincorporating.. two. spaced; and successivelyradiating: transmit-.

.. ters having the samej carrier frequency: withrthe:

signals of. one transmit-.terzbeilistone..` modulated. two-rotatabledirectional antenna.; a, receiver unit'. fork automatically.`orientingga connected Yonejo saidI directionalantennaefto astablebearing; p.o,.. sition with respect. to corr.esoondingly.-ireceivedJradio signals.. said receiver unit being; tuned. to.. the, common.carrier frequency` of the'tvvof suc.,- cessi-voirradieting;signaltransmitters'; admiro.- Siticn; indicatoru having. apair. or. indicating .ele-- monts cach. electrically comicotod,vtori-nie.L of said. dircciiferial-w antennae; for pointing out; theiranfgular. orientation; oncof Said directionalantenna normally being inlconnection. withv said receiverI unit duringv reception by. s aid unitof. unmodulated -l Signals from one of; the transmitters for giving.;directional` bearings on. a. Single. transmitted. radio' Signal; cdevice including ai Solenoid con.- ncctcdto, said unit., a.. rstsotroicontacts. oon-- ncctcdy to one of Saidv antennae and itsforienting;

1 .mcanaelid movable armatures comicctcdtcsaid;

unit. and. operatively associated; with: So1enoid... said solenoid:normally: being energized to retain its. armatures engagement with..cnc-sot of; oon..-

tacts to normally.` connect said; one antenna to;v

scid` unit during; reception: by scid, unitl or. uri.- modulatedsignals. from one of the transmitters; selectivelyoperable tone` passfilterl means. eiec.- tivcfupon rocclctionbrsaidnunt oitonemodulatcwSignals fromthe. other trcnsmittcrto effect de:

enereizcticnfoifscid solenoid tofoonnect the.otiier.'

enterica. tc. said; for obtaining individual.. bearing. indications..cricachf` oir the. transmitters.

14.2111@ radio guidance system incorporating; two; spacedVanigsuccessivclr radiating. transniitry ters having the. same carrierfrequency'withzthe'. signals of one transmitter beingtonemodulated, tworotatable directional-, .antennaep a receiver unit. for-automatically.orientingr4 agconnectedi onev of said directional antennaeto a stable'bearing- Position With rcsnectzto correspondinglyreceived?. radio fsignals.. Said receiver.' unit. beine. tuned .Y to;l the: common cernerfrequency off the; two. suc..-ccSSi/clv..radiating..sienalitrarismitters; twonosiz-J tiontransmitters. eachV connected to.v one.. of. said:A

energized to retain its armatures in engagement with one set of contactsto normally connect said one antenna to said unit during reception bysaid unit of unmodulated signals from one of the transmitters;selectively operable tone pass lter means effective upon reception bysaid unit of tone modulated signals from the other transmitter to eiectdeenergization of said solenoid to connect the other antenna to saidunit for obtaining individual bearing indications on each of 10 thetransmitters; and switching means for disconnecting the associatedindicating element from the normally unconnected directional antenna andconnecting said associated indicating element with the indicatingelement of said normally connected antenna, whereby both indicatingelements give identical directional readings corresponding to theorientation of said connected directional antenna.

WILLIAM P. LEAR.

